The Green Ocean

4 December 2013

PhD student Amy Valach, recently returned from her first visit to the tropics, describes a research project which is measuring trace gas emissions from pristine forest and her first encounters with Amazonian wildlife.

Plants emit small amounts of gases into the atmosphere called volatile organic compounds (VOCs). Out of a huge range of different compounds, one single compound called isoprene makes up more than half of the global emissions.

Not all plants emit isoprene though, most of it comes from broadleaf trees and shrubs in the tropics where the temperatures are high and there is lots of sunlight. As soon as these compounds are released into the atmosphere they start to react with other chemicals, the products of which can help to form organic aerosols. These aerosols can change the amount of sunlight reaching the surface and so affect the climate.

There are also other outcomes of the chemical reactions of isoprene which affect air quality. If there are other pollutants from human activities such as from traffic or agriculture, isoprene can contribute to the formation of ground level ozone, which is a pollutant that is harmful to humans, animals and even plants.

Large areas of forest in the tropical zone are being converted to agriculture or succumbing to urban expansion at a higher rate than any other region in the world. It is therefore important to measure a natural baseline of isoprene and other volatile organic compounds (VOCs) in a pristine area which is unaffected by emissions from human activities, so we can better understand the natural surface-atmosphere interactions.

This project is going to form part of my PhD thesis and after months of waiting, finally my colleague, Dr. Emily House, and I travelled to Manaus in August 2013. Our colleagues, Drs. Marvin Shaw and Brian Davison, had gone ahead in July to unpack and setup the instrumentation. Our equipment mainly consisted of a proton transfer reaction-mass spectrometer (PTR-MS) to measure VOC fluxes from the forest canopy.

The inlet of the system is situated at the top of a 53 m triangular mast which provides continuous air sampling from above the canopy. A small addition to our setup was a camera to be installed on the tower to take regular photos of the canopy to monitor changes in leaf colour and coverage throughout the year. Although it is difficult to see such changes in an evergreen tropical forest, I am hoping to identify links between changes in leaf properties with VOC emissions.

I had never been to the tropics before and of course the strange and fantastic tropical flora and fauna attracted my attention. Many animals were recognisable but either their bright colouring or enormous size reminded of their exotic existence. Avoiding falling foot-long stick insects and adhering to the unwritten rules of jungle traffic between humans and animals (where animals, especially snakes always have right of way) spiced up the day to day work.

On the many walks along the clay access road we often found animal prints of all kinds. Between the many snake trails and paca footprints (pacas are fairly large rodents found in Central and South America), if we were lucky, we would find prints of cat paws.

As a scientist one cannot help being inquisitive and I soon picked up the hobby of hunting for animals with the tower camera prior to its deployment, which happened to be equipped with infrared (IR) –sensors. My first few attempts produced photos of a paca, but mainly pictures of sunny and windblown leaves.

Only after my third attempt was I rewarded for my patience with photos of a small cat (possibly an ocelot), a confused-looking tapir and most stunning of all, a jaguar. The pictures were taken within 1.5 km of our field camp and just show how intact and undisturbed this area of forest still is.

Shortly after capturing these images we installed the camera on the mast for its intended purpose. Climbing the tower is always a thrill, not to mention the relief of a cool breeze! One is completely surrounded by a green sea of trees and does not need much imagination to feel the vast expanse of this vast green ocean, the Amazon rainforest.

The measurements are on-going and we hope to be able to determine a long term background baseline for various VOCs to support atmospheric chemistry models. This will require many more trips and I am excited to discover more of the vast natural beauty of this unique ecosystem.

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About the Author

Dr Amy Valach is an atmopheric scientist working for the British Antarctic Survey. She has a PhD in Environmental Sciences and an Ecology degree from Lancaster University. Her area of research interest is to understand the effects of surface exchanges to the atmosphere in the Earth system.